small fix

alkatorapi/views.py

@@ -315,6 +315,7 @@ web: https://alkator.cz""",
     elif paid == 'CANCELLED' and not invoice.paid:
         for ip in InvoiceProduct.objects.filter(invoice=invoice):
             ip.product.quantity += ip.quantity
+            ip.product.save()
             ip.delete()
         invoice.delete()
     return HttpResponse(status=200)